Hmm a 6th Pokemon. It looks like you need another attacker. You need someone to resist for when they try and take down the Ferrothorn. You have a couple options.
Greninja
Dark Pulse
Ice Beam
Scald
Grass Knot
Nature: +SpA/-Atk
Focus Sash/Life Orb
252Spe 252Atk 4Hp
OR
Talonflame
Brave Bird
Flare Blitz
U-Turn
Flame Charge/Aerial Ace/???
144 HP/252 Atk/112Spe
Choice Scarf/Leftovers
Nature: +Atk/-SpA
Those are just two Pokemon I like. However, I've been using this recently and it's a great water sweeper.
Crawdaunt
Aqua Jet
Crabhammer
Knock Off
Brick Break/Aerial Ace/Swords Dance
Life Orb
Adaptability
Adamant Nature
252Spe/252Atk/4HP
I'm not all that great, though, so it's up to you.
To expand, better sets for each. Greninja needs all the power it can get, so Hydro Pump is the better option over Scald. Scald is better off for defensive Pokemon, IMO:
-Hydro Pump
-Ice Beam
-Extrasensory
-Dark Pulse/Hidden Power (Fire/Grass)/Grass Knot/Spikes
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Focus Sash
Ability: Protean
Better sets for Talonflame here. Flame Charge and Aerial Ace aren't that strong and Talonflame needs the raw power of both Flare Blitz and Brave Bird. Sure, they induce recoil, but that's what Roost is for:
-Flare Blitz
-Brave Bird
-U-turn
-Tailwind/Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Swords Dance
-Flare Blitz
-Brave Bird
-Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Bulk Up
-Brave Bird
-Roost
-Taunt/Will-o-Wisp
Nature: Careful
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gale Wings